The present invention relates to a thrust reverser for a turbofan-type turbojet engine having the capabilities of also varying the exhaust cross-section of the cold flow air duct.
In turbofan-type turbojet engines, a cowling is disposed generally concentrically about the hot gas exhaust duct of the turbojet engine so as to define a cold flow air duct therebetween. The cold flow air duct directs air from a turbofan driven by the engine in a direction generally parallel to the longitudinal axis of the engine, so as to augment the thrust of the turbojet engine.
In such engines having a sufficiently high by-pass ratio, it is known to provide a thrust reversing device which acts only on the air passing through the cold flow air duct. The thrust reverser may comprise movable cowl portions adapted to be axially movable along the longitudinal axis of the turbojet engine so as to cover and uncover thrust reversing deflection vanes mounted on a stationary portion of the cowl. Flaps are typically present on the interior surface of the movable cowl portions so as to block the cold flow air duct and to direct the air generally laterally outwardly through the deflection vanes to provide the requisite thrust reversing force. Typically, the movable cowl portions are axially moved in a downstream direction to uncover the deflection vanes.
Generally the movable cowl portions comprise semi-cylindrical portions located on either side of an axial plane passing through the longitudinal axis of the engine and are provided with actuators to move them in their axial directions. Link rods may be connected between the flaps and a stationary portion of the engine structure such that axial movement of the cowl portions also causes the flaps to assume their blocking positions. Typical examples of such thrust reversers can be found in U.S. Pat. No. 3,500,645 to Hom and European Patent Application Ser. No. 0 109 219.
The known thrust reverser designs have proven generally successful, especially when the turbojet engine is operating in the forward thrust mode under steady state, cruising conditions. The movable cowl portions in combination with the stationary cowl provide substantially continuous, aerodynamic internal and external cowl surfaces so as to provide efficient air flow in the cold flow air duct and over the external surface of the cowl.
The known thrust reversing systems do not have the capabilities of adjusting the cross section of the cold flow air duct. This presents a problem during full power operation of the turbojet engine, such as during aircraft take-off or climbing, when it would be advantageous to provide a greater exhaust cross-sectional area for the cold flow air duct to achieve the full thrust augmentation benefits of the turbofan.